1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to blocking of light in a top-gate-type thin film transistor formed for every pixel.
2. Description of the Related Art
A liquid crystal display device is constituted such that a first substrate on which thin film transistors and the like are formed and a second substrate on which color filters and the like are formed are arranged facing each other with a liquid crystal layer sandwiched therebetween. Particularly, as shown in FIG. 14, in a conventional liquid crystal display device where each thin film transistor has the double gate structure constituted of two top-gate-type thin film transistors TFT1, TFT2, a pixel electrode PX is formed for every region surrounded by scanning signal lines (gate lines) GL which extend in the X direction and are arranged parallel to each other in the Y direction and video signal lines (drain lines) DL which extend in the Y direction and are arranged parallel to each other in the X direction thus forming a pixel region. Two thin film transistors TFT1, TFT2 which are connected in series are formed in the vicinity of a region where the gate line GL and the drain line DL intersect with each other, and a video signal is supplied to the pixel electrode PX from a source electrode ST of the thin film transistor TFT2 via these two thin film transistors TFT1, TFT2. In such a constitution, as can be understood from FIG. 15 which is a cross-sectional view taken along a line K-K′ in FIG. 14, a semiconductor layer PS which forms two thin film transistors TFT1, TFT2 is configured to be laminated on a side closer to the first substrate SUB1 than to the gate line GL which is formed of a metal thin film or the like. In view of such structure, for suppressing a light leak current generated due to the incidence of a backlight light BL indicated by an arrow into the semiconductor layer PS, there has been proposed the forming of a light blocking layer for blocking the backlight light BL. In FIG. 15, insulation films PAS1 to PAS5 are thin film layers which insulate the respective thin film layers such as the semiconductor layer PS, and the thin film layer which constitutes the uppermost layer of the first substrate SUB1 is an orientation film ORI.
As a liquid crystal display device where the light blocking layer is formed, there has been known a liquid crystal display device described in JP 2001-33822 A, for example. The liquid crystal display device described in JP 2001-33822 A is configured such that when one thin film transistor is arranged for every pixel, an area of the light blocking layer is formed smaller than an area of a semiconductor layer, and the light blocking layer is arranged so as to cover a source electrode side of the thin film transistor, that is, a side of the thin film transistor which is connected to a pixel electrode. Further, when the liquid crystal display device uses a top-gate-type thin film transistor having the double gate structure, blocking of light is applied to a thin film transistor on a side closer to the pixel electrode by a blocking film.